This invention relates to an overload release clutch and, more particularly, the invention is concerned with providing a clutch system capable of transmitting rewind torque and pretension of a tape for use in an aircraft arresting system for land or ships based hook-equipped aircraft.
Most currently available arresting systems are composed of two identical arresting units emplaced one on each side of the runway and an interconnecting deck pendant - purchase tape assembly that stretches across the runway. Each arrester unit includes an energy absorber module which is designed to be either directly ground emplaced or secured to the ground by means of earth anchors. Also, the arrester unit may be mounted in situ on concrete foundations with anchor bolts. Suitable weather protection is provided to prevent freezing rain and snow buildup from interfering with the proper operation of the functional elements.
In a typical arrester unit, the energy absorber module includes a runway-edge sheave assembly through which the primary purchase tape is reeved. This tape then stretches for some 60 to 500 ft (depending on the requirements of each particular installation) at right angles to the runway until it makes contact with a stationary sheave, mounted on the baseplate of the energy absorber module which changes the direction of the tape. From here the tape runs through a linear brake, down a protective tube until it reaches the movable sheave block, through which it is reeved. From this block the primary tape runs back toward the energy absorber module so that a loop, called the auxiliary payout loop, is formed. Then the tape passes through a set of brushes, over another stationary sheave, and finally enters the primary tape reel. The primary tape reel is keyed to the vertical cantilevered end of an energy absorber shaft which is for example, a rotary hydrodynamic device whose cylindrical housing is bolted to the base plate of the energy absorber module. A secondary reel having caliper-disk type dry friction brakes is also included in the system for operation during the aircraft arrestment.
A diesel engine mounted on the base plate provides power for rewinding the tape on the primary storage reel. A transmission including a torque converter and a back-stop clutch is bolted to the bell housing of this engine. The output shaft from the transmission is coupled to a worm gear reducer having an output shaft which carries a sprocket for transmitting the rewind power to the primary reel.
Between the back-stop clutch and the primary tape reel it is necessary to provide an overload clutch device which is capable of transmitting rotary motion at zero slip when the resisting torque at the output shaft is below a certain critical value known as the tripping torque, and of disengaging suddenly once the resisting torque level exceeds the tripping torque. Upon disengagement, the output shaft should freewheel in either direction at an essentially zero parasitic torque while the input torque also drops to zero. The hereinafter described overload clutch will operate in the manner described and is particularly useful in an aircraft-arresting system.